Abstract:

The evaporation of sessile droplets plays an important role in various applications. However, numerical simulation methods still need to be explored to investigate the influence of electric fields on the internal flow and heat transfer of droplets. A multi-relaxation lattice Boltzmann model was proposed by combining the phase change and leakage dielectric models, and was compared and verified with experimental results. This model was used to study the influence of electric field on the morphological changes, electric field force distribution, flow and heat transfer during the evaporation process of droplets. The results showed that the droplets were stretched along the direction of the electric field, and their height increased with the electric capillary number (Ca_E) while the contact diameter of the droplet decreased. The electric field expanded the range of the internal flow of the droplets to render their flow more uniform. When Ca_E=0.4, the value of Peclet number was 3.3 times that in the absence of the electric field, but the internal flow of the droplets had no significant effect on the temperature distribution of the system. As the electric field stretches the droplets, the thermal resistance to heat transfer increases and therefore the time required for evaporation increases. The effect of electric field is to change the geometric characteristics of droplets, and the increase of contact line densityis the main reason affecting the average heat flux.

Key words: charged droplet, evaporation, heat transfer, mesoscale, evaporation rate, lattice Boltzmann method

摘要：

固着液滴蒸发在各种应用中起着重要作用，然而数值模拟研究电场对蒸发液滴内部流动及传热影响还有待探索。结合相变和漏电介质模型提出了一个多松弛格子Boltzmann模型，并与实验结果进行了对比验证。运用该模型研究了电场对液滴蒸发过程的形态变化、电场力分布、流动和传热的影响。结果表明，液滴沿电场方向被拉伸，其高度随电毛细数（Ca_E）的增加而增加，电场扩大了液滴的内部流动范围，使其流动更加均匀。当Ca_E=0.4时，Peclet数是无电场时的3.3倍，但相对于热传导，液滴的内部流动对温度分布没有显著影响。由于电场拉伸液滴，导致传热热阻增加，因此蒸发所需的时间增加。电场的作用是改变液滴几何形态，而接触线密度的增加才是影响平均热通量的主要原因。

关键词: 荷电液滴, 蒸发, 传热, 介尺度, 蒸发速率, 格子Boltzmann方法